Réaumur is the remains of a lunar crater located on the southern edge of Sinus Medii. It lies to the northwest of the large walled plain Hipparchus, and east of Flammarion. To the south is Gyldén, and farther to the south-southwest is Ptolemaeus. The rim is heavily eroded, and the northern half consists of little more than a series of low ridges in the mare. (wikipedia entry)
